JPH08201523A - Stationary Radon / Tron Discrimination Concentration Meter - Google Patents

Abstract

(57) [Summary] [Structure] The plastic film detector 7 for detecting α-rays on the upper and lower surfaces is supported by the through-hole portion 32 of the fixed base 3, and the upper bowl portion 1 and the lower bowl portion having a diameter smaller than this. The two types of hollow hemispheres with the part 4 are respectively arranged above and below the fixing table 3 so as to cover the plastic film detector 7, and the upper bowl part 1 is allowed to ventilate with the outside air, and the upper bowl part 1 and A stationary radon / thoron discriminating concentration measuring device characterized in that the hollow hemisphere of the lower bowl portion 4 is ventilated through a ventilation hole. [Effect] It is possible to measure the radon concentration with high accuracy without the influence of thoron. By optimizing the electrochemical etching time and the container shape to improve the measurement sensitivity, the outdoor radon concentration (about 5 Bqm ^-3 ) can be measured even for 6 months.
Can be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a static radon / thorone discriminating concentration measuring device. More specifically, the present invention relates to a static (passive) radon / thorone discriminating concentration measuring device that eliminates the influence of thoron in the radon concentration measurement and enables highly accurate indoor and outdoor radon concentration measurement.

[0002]

2. Description of the Related Art In the evaluation of the effect of environmental radiation, indoor and outdoor radon concentration measurement has been attracting attention, and various methods and devices have been attempted to measure this. This radon (Rn) is an element with atomic number 86, and this radon is the colorless and odorless heaviest gas (density; 9.96 kg / m ³ ), and is a rare gas with extremely low abundance in the global environment. Is. Radon radioisotopes from uranium series (parent nuclide; ²³⁸ U)
²²² Rn is produced and thorium series (parent nuclide; ²³² T
²²⁰ h is generated from h). ²²² Rn generated from the uranium series is called a radon, and ²²⁰ Rn generated from the thorium series is called a thoron. And
Since uranium and thorium are different elements, the contents of uranium and thorium in soil, water, and building materials that control the indoor and outdoor concentrations of radon and thoron are different, and radon and thoron are discriminated and measured independently. I have to. However, conventionally, with a static (passive) type measuring device, only the radon concentration can be measured, and it has been impossible to discriminate thoron from radon.

For this reason, in the case of the conventional method and apparatus, that is, the above-mentioned static (passive) type measuring instrument, the influence of thoron cannot be eliminated in the radon concentration measurement,
There was a great limitation in improving the measurement accuracy. Therefore,
The present invention solves the above-mentioned drawbacks of the prior art, and influences of thoron in the measurement of radon concentration (tron noise).
It is an object of the present invention to provide a new stationary type radon-thoron discriminating concentration measuring device which enables the removal of the above-mentioned substances and can measure the radon concentration with higher accuracy.

[0004]

In order to solve the above problems, the present invention supports a plastic film detector for detecting α-rays on upper and lower surfaces in a through hole portion of a fixed base,
Two types of hollow hemispheres, an upper bowl and a lower bowl with a diameter smaller than this, are arranged above and below the fixing table so as to cover the plastic film detector, and the upper bowl hollow hemisphere is exposed to the outside air. Provided is a static radon / thoron discriminating concentration measuring device, characterized in that hollow hemispheres of the upper and lower bowls are ventilated through ventilation holes.

Further, according to the present invention, the fixing base is formed into a disk shape, and ventilation with the outside air is performed by an opening filter portion provided on the fixing base, and further, a detector is provided with two polycarbonate plastic films. According to a preferred embodiment, it is also configured. Hereinafter, the configuration and the measuring method using the static radon / thorone discriminating concentration measuring device of the present invention will be described as examples.

[0006]

[Example] 1. Structure of the measuring instrument Figure 1 shows an example of the structure of the radon / thorone discriminating measuring device.
Is. In this case, the material of the measuring section container can be stainless steel. The measuring instrument is a hollow upper bowl hemisphere (1) with a diameter of 120 mm, an upper bowl fixing base (2), a detector fixing base (3) (also serving as a lower bowl fixing base), and a lower bowl hollow with a diameter of 75 mm. It has a hemisphere (4).

FIG. 2 shows an example of the structure of the detector fixing base (3) (diameter 146 mm, thickness 3 mm). A circular groove (31) for fixing the detector (diameter 50 mm, depth 1 mm) is provided in the center of the fixing base, and a through hole (3) is provided at the center thereof.
2) (20 mm diameter). A ventilation hole (33) (diameter 1 mm) between the upper bowl hollow hemisphere (1) and the lower bowl hollow hemisphere (4) is formed on the outer periphery of the detector fixing groove (31).
It is provided individually. On its outer circumference, a circular ventilation hole (33) for taking in external air into the upper bowl hollow hemisphere (1)
(Diameter 14 mm, dust removal filter (Schleicher Germany
and Schuell Glass Fiber filter No.6)) is installed.

FIG. 3 illustrates the structure of the upper bowl fixing base (2) (diameter 146 mm, thickness 2 mm).
There is a through hole (21) having a diameter of 120 mm in the center, and a circular punching metal (5) (diameter 120 mm, thickness 2 mm, made of stainless steel) is fitted and welded. As shown in FIG. 1, the upper bowl fixing base (2) and the detector fixing base (3) (which also serve as the lower bowl fixing base) are closely fixed by a short rubber ring (6). ing. 2. α-ray solid track detector As shown in FIG. 1, the above-mentioned measuring instrument is equipped with a plastic film detector (2) for detecting an α-ray solid track in its detector fixing groove (31).

The material of this α-ray solid track detector is, for example, poly carbonate (manufactured by Mitsubishi Gas Chemical Co., Inc., Iupi
lon S-2000 type). The shape shall be circular (diameter 50 mm, thickness 0.3 mm). The two films are back to back and fixed to the center of the detector fixing base with a metal adhesive tape. 120mm diameter upper bowl hollow hemisphere (1)
The film (71) exposed on the side is referred to as Tron radon sensing film, and the film (72) exposed on the lower bowl hollow hemisphere (4) side having a diameter of 75 mm is referred to as radon sensing film. 3. Radon / Tron concentration discrimination measurement 3-1 Measurement of Tron concentration in the container by ventilation rate design Radon has a half-life of about 3.82 days (decay constant λ = 0.00756
h ⁻¹ ), which emits 5.49 MeV α rays and emits ²¹⁸ Po (R
aA; solid). On the other hand, the half-life of tron is 55.6 seconds (decay constant λ = 44.9 h ⁻¹ ), and α rays of 6.29 MeV are emitted to become ²¹⁶ Po (ThA; solid). The filter attached to the ventilation hole prevents intrusion of suspended dust (aerosol) into the measurement container. As a result, only radon-tron in the gas state enters the measuring container. The penetration rates of radon gas and thoron gas into the measurement container are 1) the time during which the radon and thoron can maintain a gas state, that is, the value of the decay constant λ, and 2) the time required to enter the measurement container, that is, the ventilation rate J. It is determined by the value of (unit: h ⁻¹ ). The radon (tron) concentration ratio (R) inside and outside the measurement container is calculated by the following equation (A) from the decay constant and ventilation rate (steady solution).

R = J / (J + λ) (A) In the case of radon, since the decay constant λ is a very small value, R hardly changes regardless of how the ventilation rate J is set. On the other hand, in the case of TRON, since the decay constant λ is a very large value, R greatly changes depending on the ventilation rate J. This is the basic principle of Radon-Tron discrimination by ventilation rate.

As shown in FIG. 1, the above-mentioned static radon / tron concentration measuring instrument of the present invention has a measurement container internal space having a hollow hemispherical internal space (anterior chamber) (10) having a diameter of 120 mm and a diameter of 75 mm. It is structured so as to be separated into a hollow hemisphere inner space (rear chamber) (40). The antechamber (10) is connected to the outside of the measurement container through eight ventilation holes having a diameter of 14 mm, and has a structure for taking in both radon and thoron gas. Front room (1
0) and the rear chamber (40) are ventilation holes (32) with a diameter of 1 mm.
It is a structure that mutually ventilates through one. In this structure, the ventilation rate J (h
FIG. 4 shows the results of the examination of ( ^-1 ) with a gas chromatograph (carrier gas; nitrogen) using sulfur hexafluoride (SF ₆ ) gas as a sample gas. In addition, the antechamber (1
FIG. 5 shows the results of similarly examining the ventilation rates J (h ⁻¹ ) of 0) and the rear chamber (40). From the slope of the regression line in Fig. 4, the ventilation rate between the outside of the measurement container and the measurement chamber front chamber (10) (120 mm diameter hollow hemisphere) was 15.89 ± 0.087.
It is estimated to be (h ^-1 ). Further, from the slope of the regression line in FIG. 5, the ventilation rate J between the front chamber (10) (hollow hemisphere with a diameter of 120 mm) and the rear chamber (40) (hollow hemisphere with a diameter of 75 mm) J
Is estimated to be 0.378 ± 0.005 (h ^-1 ).

From the above formula (A), the diameter 120
The penetration rates of radon and thoron into the millimeter hollow hemisphere (anterior chamber) (10) are calculated as follows. Radon ( ²²² Rn) 99.95% Tron ( ²²⁰ Rn) 26.14% Radon and Tron that have penetrated into the hollow hemisphere with a diameter of 120 mm (front chamber) (10) are now in the hollow hemisphere with a diameter of 75 mm (rear chamber) (40). The invasion rate is calculated from the equation (A) as follows.

Radon ( ²²² Rn) 98.04% Tron ( ²²⁰ Rn) 0.835% By integrating the results of two experiments, the penetration rates of radon and thoron into the hollow hemisphere (rear chamber) (40) with a diameter of 75 mm are as follows. Estimated. Radon ( ²²² Rn) 97.99% Tron ( ²²⁰ Rn) 0.218% While in the same measurement container, the front chamber (10) (diameter 12
0 mm hollow hemisphere) tron concentration (concentration outside the container is 26.14)
%) And the thoron concentration in the rear chamber (40) (hollow hemisphere with a diameter of 75 mm) (0.218% of the concentration outside the container) have a large difference, and by utilizing this difference, the radon concentration and the thoron concentration are discriminatively measured. can do. 3-2 Radon / tron concentration discrimination measurement by α-ray energy difference (a) α-ray solid track (track) detection α-rays (helium nuclei) give energy to the substance while proceeding straight through the substance, and finally Stop in the substance. The moving distance of α-rays from the emission position to the stop position is called (average) range, and is represented as a function of α-ray energy at the time of material incidence. When polycarbonate (solid) is used as the detector, its average range can be estimated using a converted value of 0.86 (μm / cm) with air at 15 ° C. as a reference. This is because the energy lost by α rays when moving 1 cm in air at 15 degrees Celsius is 0.86 in polycarbonate.
It is equal to the energy lost when moving by μm.

The path along which α rays move in a solid substance can be called a “solid nuclear track.” In this solid track, the ionization and
The molecular polymerization (polymer) structure is destroyed due to the exciting action. The characteristic of energy application of heavy charged particles such as α rays is that deceleration immediately before stop (just before the average range is exhausted),
It is to give most of the energy to a very limited short range. Ionization / excitation amount per unit length
Here, the distance to the position (Bragg peak) where the specific ionization rapidly increases is referred to as the "effective average range" for convenience.

When the polycarbonate film is immersed in a mixed solution of a strong alkaline solution (8N potassium hydroxide solution) and ethyl alcohol, the surface of the film is gradually dissolved by a chemical action (etching). The solid tracks (tracks) of α rays are easily dissolved because the molecular polymerization structure is destroyed, and as a result, mortar-shaped chemical etch pits (diameter of 0.1 μm or less) are formed along the tracks.

When the dissolution of the polycarbonate film surface by etching further progresses and the α-ray solid track (track) corresponding to the effective average range is etched, the chemical etch pit is rapidly expanded to a diameter of about 2-3 μm, and Can be recognized under the microscope. The chemical etch pits are further expanded as the etching continues, but solid tracks (tracks) grow when they grow to a diameter of about 5-6 μm.
The average range of is exhausted, and growth stagnates. After that, the corners of the chemical etch pits are removed as the etching progresses,
It becomes a round etch pit (diameter of about 5-6 μm). Once formed, the circular etch pits are preserved as they are, without changing, no matter how much chemical etching is performed thereafter.

On the other hand, when the α-ray solid track (track) corresponding to the effective average range is applied with a high voltage and high frequency AC electricity during the chemical etching (electrochemical etching), it is accompanied by a rapid expansion of the chemical etching pit. Dielectric breakdown is caused, and the chemical etch pits are physically / chemically destroyed / expanded. As a result, the α-ray solid track becomes an electrochemical etch pit (diameter of about 40 to 300 μm) that can be visually observed.

When chemical etching is carried out before electrochemical etching, α solid tracks having a short effective average range (low incident energy) are converted into round etch pits.
In the circular etch pits, the destruction of the molecular structure due to ionization / excitation of α-rays is cleaned up by dissolution, so even if electrochemical etching is performed, dielectric breakdown is not caused and the circular etch pits are preserved as they are. It

From the above, the α-ray solid track (track) left on the surface of the polycarbonate film is detected in the form of either a round etch pit or a chemical vapor etch pit. That is, A) When the α-ray track corresponding to the effective average range is chemically etched → Round-shaped etch pit (diameter of about 5-6 μm) B) The α-ray track corresponding to the effective average range is electrochemically etched Case → Electrochemical etch pit (diameter 40-3
(B) Radon / tron discrimination based on the difference in emitted α-ray energy In this measuring instrument, α solid tracks (tracks) are detected and counted as electrochemical etch pits. Since the detectable etch pit diameter is 40 μm or more, round etch pits (diameter of about 5 to 6 μm) are not detected.

The polycarbonate film fixed to the center of the measuring instrument and irradiated with α-rays from Radon-Tron is subjected to chemical etching for a certain period of time, and then electrochemically etched. Due to the chemical etching, the α solid track (track) having a short effective average range (low incident energy) becomes a circular etch pit and is removed from the detection target. Therefore, the length (time) of chemical etching determines the lower limit of detection of the incident energy of α rays (normal incidence). The length (time) of the electrochemical etching that is performed subsequent to the chemical etching determines the detectable energy region of the α-ray upon incidence.

In the case of etching a thoron / radon sensing film, by performing chemical etching for a long time and then performing electrochemical etching, α rays emitted from thoron and nuclides (from α rays emitted from radon and daughter nuclides) The overall energy of emission is high). When etching the radon sensing film, chemical etching is performed for a short time, and then electrochemical etching is performed, so that α-rays emitted by radon and nuclides (total emission from α-rays emitted by thoron and daughter nuclides) Sensitivity (for low energy) can be increased.

The above is the explanation of the principle of the discriminating measurement method of the α solid track by the energy upon film incidence in the apparatus of the present invention. 4 Optimal design of the shape and structure of the measuring container and etching time
Optimization Accordingly, next, already the configuration of the apparatus of the invention as described above, also a method for its optimization for the etching time, for its effect will be described. 4-1 Design conditions for container shape Radon and thoron that enter the detection container emit α-rays and then decay to become daughter nuclides. It adheres to the inner surface of the measuring container by diffusion. Since the daughter nuclide is positively charged, it is affected by the electric field, but since the measurement container is made of a conductive material (stainless steel), no electric field is generated on the inner surface of the container.
The daughter nuclide uniformly attaches to the inner surface of the measurement container. Since the measurement container has a structure having two types of hollow hemispheres, the distance between the deposition position of the daughter nuclide and the polycarbonate detector is fixed to the radius of each hemisphere container.

Since the gases radon and thoron are distributed almost uniformly in the space inside the container, the linear distance between the position where the α-rays are emitted from the radon gas and the thoron gas and the position where they are incident on the polycarbonate film are the respective hemispheres. Limited to the radius of the container. 4-2 Design conditions for etching time The following solutions are used for chemical etching and electrochemical etching.

Solution A) Polycarbonate film (exposed surface side) etching solution Mixed solution of 8N (molar concentration) KOH (potassium hydroxide) solution and ethanol (mixing ratio is KOH80 by volume)
%, Ethanol 20%) B solution) Polycarbonate film (back side) electrolytic solution 1N (molar concentration) KOH (potassium hydroxide) solution The relationship between the temperature of the etching solution A and the surface etching rate of polycarbonate (vertical direction) is shown in FIG. It was shown to. From the slope of the straight line, the etching rate (vertical direction) of the 8N KOH mixed solution is 3.57 (standard deviation 0.02) μm per hour (30 ° C.).

An electrode is inserted into the etching solution and a high frequency (2
By applying an alternating current (sinusoidal wave) of 000 Hz) and high voltage (effective voltage 800 V), it is possible to shift from chemical etching to electrochemical etching. It has been experimentally confirmed that the chemical activity of the etching solution does not change for 7 hours continuously. It has also been experimentally confirmed that, when electrochemical etching is performed on a polycarbonate film having a thickness of 0.3 mm, through-hole perforation occurs in 3.5-4 hours after baking, making it impossible to continue the electrochemical etching. 4-3 Optimum design of measuring instrument performance (detection sensitivity, discrimination ability) Under the conditions shown in 4-1 and 4-2,
A) improved detection sensitivity to radon and thoron, B)
The hemispherical vessel diameter and etching time were optimally designed considering the advantages and disadvantages of improving the discrimination ability of radon and thoron. A Monte Carlo calculation program was developed for the design. The shape of the measurement container obtained as a result of the optimization is as shown in FIGS.

Table 1 shows the etching conditions for the thoron radon sensing film and the radon sensing film. Table 2 shows the design values of the detection sensitivity (Monte Carlo calculation value) for radon and thoron of the thoron radon sensing film and the radon sensing film under each etching condition.

[0027]

[Table 1]

[0028]

[Table 2]

Table 2 and radon in each hemispherical container and
A Tron-Radon sensing filter estimated from the Tron invasion rate.
The calibration constants (design values) for Rum and Radon sensing films are
Like Tron Radon Sensing Film Radon (²²²Rn) 0.0190^{* 1} tracks cm^-2/ (Bqm^-3 d
ay) Tron (²²⁰Rn) 0.0132^{* 1} tracks cm^-2/ (Bqm^-3 d
ay) Radon sensing film Radon (²²²Rn) 0.0393 tracks cm^-2/ (Bqm^-3 d
ay) Tron (²²⁰Rn) 0.0001 tracks cm^-2/ (Bqm^-3 d
ay)^{* 1} ) The Monte Carlo calculation used in the design
-2.8 MeV for alpha-ray at electrochemical etch
Experimentally investigated the relationship between the diameter of the pit and the etching time.
It is built on the fruits. Tron Radon Senfi
In the case of Rum, α-rays with a large incident energy (2.8 M
eV or higher) is the target for detection, so a Monte Carlo meter
The calculation was performed by linear extrapolation from low energy data.
Have been. 5 Performance test results using a standard radon chamber U.S. Environmental Protection Agenc
y) The standard radon calibration chamber of
Radon comparison of stationary (passive) type radon / tron discriminator
The result of carrying out the positive experiment is shown in FIG. Slope of regression line
The calibration constants obtained from the Tran Radon sensing film (120 mm diameter hemisphere) radon (²²²Rn) 0.0299 ± 0.0017 (r = 0.984) tra
cks cm^-2/ (Bqm^-3day) Radon sensing film (75 mm diameter hemisphere) Radon (²²²Rn) 0.0395 ± 0.0053 (r = 0.919) tra
cks cm^-2/ (Bqm^-3day).

Radon of the Institute of Science and Engineering, Waseda University
Tron calibration experiments of the static (passive) type Radon-Tron discriminator of the present invention were carried out using a Tron mixed calibration chamber. The average radon concentration during irradiation time (72 hours) is
257.0 ± 9.47 Bq / m ³ , average tron concentration is 523.6 ± 80.3
Bq / m ³ . The sensitivity of the radon sensing film (75 mm diameter hemisphere) is designed to have a ratio of about 400: 1 for radon and thoron, respectively, so the thoron contribution to the electrochemical etch pit count is in this case Can be completely ignored by design.

Radon sensing film (75 mm diameter hemisphere)
FIG. 8 shows the result of calibrating the total counts of the electrochemical etch pits of No. 1 with only the radon concentration. Radon calibration constant (0.0318 ± 0.0021 tracks) obtained from the slope of the calibration line in Fig. 8.
cm ^-2 / (Bqm ^-3 day)) is the calibration constant (0.0395 ± 0.0053 tracks cm ^-2 / of the US Environmental Protection Agency standard chamber)
(Bqm ^-3 day)), and it was demonstrated that the total counts of the electrochemical etch pits did not contain tron contribution (can be ignored).

To obtain the Tron calibration constant,
It is necessary to subtract the count value of the radon contribution from the total count of the electrochemical etch pits of the radon sensing film. The radon contribution count is the radon calibration constant (0.0299 ± 0.0017 tracks) by the US Environmental Protection Agency standard radon chamber.
It is calculated by back calculation from cm ^-2 / (Bqm ^-3 day)) and irradiation time (72 hours).

The result obtained by calibrating the value obtained by subtracting the radon contribution from the total electrochemical etch pit counts of the thoron radon sensing film and calibrating only the thoron concentration is shown in FIG. This Figure 9
Tron calibration constant (0.0127 ± 0.0022 tracks obtained from
cm ^-2 / (Bqm ^-3 day)) is the design value (0.0132 tracks cm ^-2
It almost agrees with / (Bqm ^-3 )). In the Radon-Tron mixing chamber of the Waseda University Institute of Science and Technology, the thoron concentration measurement results (measured by the scintill cell) fluctuated significantly (about 15% of the average value) during the irradiation period, and the thoron concentration in the chamber was A more detailed study on the uniformity of is required.

The results of the standard Radon-Tron calibration experiment conducted by the US Environmental Protection Agency and Waseda University Institute of Science and Engineering as described above are summarized as follows. It is considered that the performance at the time of design is almost exhibited in the calibration constant of TRON. Tron Radon Sensing Film Radon ( ²²² Rn) 0.0299 ± 0.0017 tracks cm ^-2 /
(Bqm ^-3 day)) TRON ( ²²⁰ Rn) 0.0127 ± 0.0022 tracks cm ^-2 /
(Bqm ^-3 day)) Radon sensing film Radon ( ²²² Rn) 0.0395 ± 0.0053 tracks cm ^-2 /
(Bqm ^-3 day)) TRON ( ²²⁰ Rn) 0.0000 ± 0.0000 tracks cm ^-2 /
(Bqm ^-3 day))

[0035]

As described above in detail, the measuring apparatus of the present invention enables highly accurate measurement of radon concentration without the influence of thoron. Electrochemical etching time,
The shape of the container is optimally designed to improve the measurement sensitivity, so that even when measured for 6 months, the outdoor radon concentration (5 Bqm ^-3
It is possible to measure

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating a device of the present invention.

2A and 2B are a plan view and a cross-sectional view showing a detector fixing base of the device of the present invention.

FIG. 3 is a plan view and a sectional view showing an upper bowl fixing base of the device of the present invention.

FIG. 4 is a time-volume correlation diagram of SF ₆ showing the ventilation rate between the outside and the anterior chamber of the hollow hemisphere in the upper bowl.

[FIG. 5] Time of SF ₆ showing the ventilation rates of the front chamber and the rear chamber.
It is a capacity correlation diagram.

FIG. 6 is a correlation diagram with time / remaining film thickness showing the polycarbonate surface etching rate.

7 (a) and (b) are Radon calibration line diagrams.

FIG. 8 is a Radon calibration linear diagram.

FIG. 9 is a Tron calibration linear diagram.

[Explanation of symbols]

 1 Upper bowl hollow hemisphere 2 Upper bowl fixing base 3 Detector fixing base 4 Lower bowl hollow hemisphere 5 Inner punching metal 6 Rectangular rubber ring 7 Plastic film detector 21 Through hole 31 Detector fixing groove 32 Through hole 33 Ventilation hole 34 Circular ventilation hole 71, 72 Film 10 Front chamber space in hollow hemisphere 40 Rear chamber space in hollow hemisphere

Claims (4)

[Claims] 1. Two types of hollow hemispheres, an upper bowl portion and a lower bowl portion having a diameter smaller than the upper bowl portion, which support a plastic film detector for detecting α-rays on the upper and lower surfaces in a through hole portion of a fixed base. Are placed above and below the fixed base so as to cover the plastic film detectors, and the upper bowl hollow hemisphere is ventilated with the outside air, and the upper bowl and lower bowl hemispheres are ventilated through the ventilation holes. A static radon / thorone discriminating concentration measuring device characterized by being made possible. 2. The stationary radon / thorone discriminating concentration measuring device according to claim 1, wherein the fixing table is disk-shaped. 3. The stationary radon / thoron discriminant concentration measuring device according to claim 1, wherein ventilation with the outside air is performed by an opening filter portion provided on a fixed base. 4. The static radon / thorone discriminating concentration measuring device according to claim 1, wherein the detector comprises two sheets of polycarbonate plastic film.